OPTIMIZATION DRILLING PROCESS OF GLASS FIBER REINFORCED PLASTICS

NORHAIDA BINTI MOHAMAD NOOR

UNIVERSITI MALAYSIA PAHANG

ACKNOWLEDGEMENT

Politely I wish everybody in a good condition. Grateful sense goes to Allah,

The Most Beneficent and The Most Merciful on His blessing until this thesis produced

properly. With a deep sense of gratitude I would like to express my sincere thanks to

my supervisor, En. Rosdi Bin Daud and for his attention to guide me on doing this

project thesis as well and not forgotten to the En. Mohd Fadzil Faisae Bin Ab. Rashid

and Pn. Noryanti Binti Muhammad who was always help me.

I am appreciates my parents supports, my siblings and my friends who involved

during this project done. Thanks a lot. To mother and father, your pray is very

meaningful to my life.

I had tried my best to apply the knowledge that you delivered and I hope this can

show my full commitment about the project. I am also happy to present everybody who

ever involved in one way or another, made significant contributions to various process

of this project. I hope I can learn something from this project and everybody can

understand all the input inside this thesis.

ABSTRACT

Fibre reinforced composites are widely recognized for their superior mechanical

properties and advantages for applications in aerospace, defence and transportation

sectors. The material that was being chosen for this research is glass fibre reinforced

plastics. Drilling tests have been conducted on glass fiber-reinforced plastic composite

glass fibre reinforced plastic laminates using an instrumented CNC milling center.

Machining parameters such as type of drilling tool, feed rate, cutting speed, and their

influence on the thrust force are investigated. Furthermore, the quality of the holes

produced from the drilling process also must be considered with special attention paid to

the delamination damage.The damage was seeing through optimal microscope. Kistler

software was been using to get the trust force value as the output in this experiment. The

Kistler Piezoelectric Dynometer was connected to the PC of CNC machine. The function

is to measure the thrust force value. The delamination factor can be calculated by using

their equation. By using SPSS software to get the equation, the equation that was being

created is Multiple Linear Regression then come out with ANOVA analysis. This

equation is to show that the significant of the variables when drilling glass fiber. After

that, User-Defined was being used to optimize the parameter and get the optimal

condition to drill glass fiber for minimized the damages.

Abstrak

Gentian yang kukuh diketahui mempunyai cirri-ciri mekanikal yang kuat dan

mempunyai banyak aplikasi di dalam sector seperti pertahanan, pengankutan dan kapal

terbang. Bahan yang digunakan di dalam untuk penyelidikan ini ialah gentian kaca

plastik yang kukuh. Dengan menggunakan mesin kisar CNC, lubang dibuat pada gentian

kaca plastik itu. Parameter mesin seperti perkakas untuk membuat lubang, kadar

kepantasan mesin bertindak(makan), kelajuan pemusing dan daya tujahan juga turut

dikaji. Selanjutnya, kualiti lubang daripada proses membuat alur tadi akan dikaji

terutamanya pada kerosakan kawasan yang tidak berlapis. Kerosakan itu dilihat

menerusi mikroskop optik. Perisian ‘Kistler’ digunakan untuk mendapatkan nilai daya

tujahan. Kistler piezoelektrik dynometer disambungkan ke computer mesin CNC.

Fungsinya adalah untuk mendapatkan nilai daya tujahan. Perisian SPSS adalah untuk

mendapatkan formula, formula dihasilkan dari gandaan kemerosotan dan menghasilkan

analysis perbezaan. Formula ini adalah untuk menunjukkan kaitan parameter semasa

membuat lubang pada gentian kaca ini. Selepas itu, kaedah User-Defined digunakan

untuk mendapatkan keadaan yang optimum untuk mengurangkan kerosakan pada

lubang.

TABLE OF CONTENT

Page

SUPERVISOR’S DECLARATION ii

STUDENT’S DECLARATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xiii

LIST OF ABBREVIATIONS xiv

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.2 Problem Statement 2

1.3 Objective 3

1.4 Scopes 3

CHAPTER 2 LITERITURE RIVIEW

2.1 Introduction 4

2.2 Drilling Process 4

2.3 Parameters for Drilling Fiber Reinforced Plastics 5

2.3.1 Spindle speed 52.3.2 Revolution per minute 72.3.3 Feed Rate 82.3.4 Trust Force and Torque 8

2.4 Measurement of Thrust Force and Torque 11

2.5 Tool Material and Geometry 12

2.6 Hole Quality and Part Performance 13

2.7 Delamination Size Measurement 15

CHAPTER 3 METHODOLOGY

3.1 Introduction 20

3.2 Problem identification and Solving 20

3.3 Material 21

3.3.1 Fiber Reinforced Plastic 213.3.2 Application 233.3.3 Construction Method 23

3.3.3.1 Fiber Hand Lay- Up Operation 233.3.3.2 Fiberglass Spray Lay-Up Operation 243.3.3.3 Pultrusion Operation 24

3.3.4 Material Preparation 24

3.4 Machine 26

3.5 Experiment Procedure and Test Analysis 27

3.4.1 Experiment Planning 273.4.2 SPSS and User-Defined Method 293.4.3 Experiment Procedure 31

3.6 Experiment Equipment 33

3.6.1 Kistler Piezoelectric Dynometer 333.6.2 Vernier Caliper 34

CHAPTER 4 RESULT AND DISCUSSION

4.1 Introduction 36

4.2 Results by Using Kistler Piezoelectric Dynometer 36

4.2.1 Graph Tool 1=HSS 374.2.2 Graph Tool 2=Coated Carbide 434.2.3 Graph Tool 3=Carbide 50

4.3 Output Value and the Fd From Experiment Result 57

4.4 Multiple Linear Regressions 59

4.4.1 Removed Method 604.4.2 Backward Method 614.4.3 Forward Method 624.4.4 Stepwise Method 634.4.5 Equation Multiple Linear Regression 65

4.5 Optimization Using User-Defined Method 66

CHAPTER5 CONCLUSION AND RECOMMENDATION

5.1 Conclusion 68

5.2 Recommendation 69

REFERENCES 70

APPENDIX 72

A Stretching the drawing using the Master Cam Software 72

B Glass fiber reinforced plastic before cutting (103 mm x 103 mm) 73

C HAAS- CNC Milling Center Machine 73

D Kistler Piezoelectric Dynometer 74

E Solution from DX-7 software 74

F Gantt chart 78

LIST OF TABLE

Table No. Page

3.1 Experiment data for different tools of drills 28

4.1 Average for Diameter Delamination zone, Da 57

4.2 Result Output 58

4.3 Variable Entered/ removed 60

4.4 Model Summary for Removed method 61

4.5 Variable Entered/ removed- Backward 61

4.6 Model Summary for Backward Method 62

4.7 Variable Entered/ removed- Forward 62

4.8 Model Summary for Forward Method 63

4.9 Variable Entered/ removed- stepwise 63

4.10 Model Summary for Stepwise Method 64

4.11 ANOVA for stepwise method 64

4.12 Coefficient for Fd Equation 64

4.13 Comparison between experiment value and by equation 65

4.14 Goal for Machining Parameters 67

4.15 Solutions for 3 combinations of categoric factor levels 67

LIST OF FIGURE

Figure No. Page

2.1 Principal aspects to be considered when drilling fibre reinforced 5

Plastics.

2.2 Cutting speeds and feed rates typically employed when drilling 7

polymeric composites with high-speed steel (HSS) and tungsten

carbide (WC) drills.

2.3 Influence of feed rate on the specific cutting coefficient (kf) 9

associated to the thrust force

2.4 Influence of feed rate on the specific cutting coefficient (km) 10

associated to torque.

2.5 Set-up for measurements the thrust force and torque. 12

2.6 Tool materials used to drill polymeric composites. 13

2.7 Photographs show the delamination for various composites 17

(a) and (b) woven/epoxy (c) chopped and (d) continuous winding.

2.8 Feed variation along the hole depth for delamination-free 19

in drilling cross-winding composite, n=1850 rpm.

2.9 Distance X vs. push-out delamination in drilling cross-winding 19

composites

3.1 Schematic work piece mounted on the dynamometer. 32

3.2 Example measuring using vernier calliper 34

LIST OF SYMBOL

P Population regression

Y Dependent variable

μ Mean respond

σ Standard deviation

ε Error

LIST OF ABBREVIATIONS

Da Diameter of delamination zone

Do Diameter of tool of drill

Fd Delamination factor

GFRP Glass fiber reinforced plastic

CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

Advanced composite materials such as fiber reinforced plastics (FRP) are

recognized as excellent materials for some structural components and are being

increasingly used in various applications such as aircraft, ships, automobiles, machine

tool and sports equipment, due to their excellent properties such as high specific

strength, high specific stiffness, high damping, low thermal expansion, good

dimensional stability and an unusual combination of properties not obtainable with metal

alloys. As structural materials, joining of composite structures could not be avoided. The

efficiency of mechanical joint is largely dependent on the quality of machined holes [1].

The drilling parameters and specimen parameters evaluated were spindle speed,

feed rate, and types of drill. A series of experiments were conducted using CNC milling

center to machine the composite laminate specimens at various cutting parameters. The

experimental results indicated that the types of tool, feed rate and cutting speed are

reckoned to be the most significant factors contributing to the delaminating and other

damages.

Using Design of Experiment, DOE, there have 27 number of test. Three types of

tool was been selected that is High speed steel HSS, coated carbide and solid carbide.

For every tool, there have 9 test of hole with different of machining parameters. In this

experiment the output is the thrust force and delamination. By using Piezoelectric

Dynometer connected to the PC at CNC milling machine the value of thrust force and

torque can get by install the Kistler software. The delamination can be analyzing using

delamination factor. The delamination factor is the ratio of diameter delamination area to

the diameter of hole. The size of diameter hole is equal to the diameter of drill 6mm.

Due to their anisotropy, and non-homogeneity, FRP cause some problems in

drilling such as fiber breakage, matrix cracking, fiber/matrix debonding, fiber pull-out,

fuzzing, thermal degradation, spalling and delamination. Among the defects caused by

drilling, delamination is the most critical. Delamination can result in lowering of bearing

strength and can be detrimental to the material durability by reducing the structural

integrity of the material resulting in long-term performance deterioration [1]. The special

attention damages to the hole quality is delamination, but in this experiment the other

damages will be investigate.

Analysis of variance (ANOVA) is used to study the effect of process parameters

on machining process. The purpose of the analysis of variance (ANOVA) is to

investigate the design parameters significantly affect the quality characteristic of a

product or process. To test the significant of the parameters on machining process the

equation of the output must being created. Here only one output was been selected that

is delamination factor, Fd. By using SPSS software, the Multiple Linear Regression

equation will be created.

Damage that developed during drilling process has to simulate using User-

Defined method. The optimization result will show the best condition to drilling glass

fiber where at this condition the damages will be minimized.

1.2 Problem Statement

There is several problems from this research, normally to machining of fiber-

reinforced composites is difficult due to diverse fiber and matrix properties, fiber

orientation, inhomogeneous nature of the material. Thus, when drilling the fiber

reinforced plastic composite may produce several kinds of damage. The most

seriously is the delamination. To investigate the damage effects of drilling an

optimization technique is employed. Appropriate control parameters are chosen to

narrow the scope of study such as spindle speed, feed rate and three types of tools and

the main outputs investigated are thrust force and delamination.

1.2 Objective

I. To get optimal condition for drilling glass fiber reinforced plastics.

II. To analyze the data of experiment by using Multiple Linear Regression

III. To analyze the damages occur at the hole with special attention is

delamination.

1.3 Scope

A research about the damages at the hole of drilling glass fibre reinforced plastic

composite and gets the optimal parameters to be used to drill glass fiber.

CHAPTER 2

LITERATURE RIVIEW

2.1 INTRODUCTION

To select cutting parameters for damage-free drilling in glass fiber reinforced

composite material. The optimization objective includes the contributing effects of the

drilling performance measures such as feed rate, spindle speed, damage at the surface,

and drilling thrust force.

2.2 DRILLING PROCESS

Drilling of holes in composite materials is a very common process in the

assembly of aerospace and automotive composite structures. With regard to the quality

characteristics of drilled composites, some of the problems encountered include surface

delamination, internal delamination, fiber or resin pullout, hole shrinkage, last ply

damage, hole surface roughness, and higher tool wear due to abrasion by hard fibers. In

order to minimize these machining problems, similar to metals, there is need to develop

scientific methods to select cutting conditions for damage-free drilling of composite

materials. Most previous work focused on optimization of parameters for machining

metallic materials.

In order to overcome these difficulties it is necessary to develop procedures to

select appropriate cutting parameters, due to the fact that an unsuitable choice could lead

to unacceptable work material degradation.

Figure 2.1 shows that factors such as cutting parameters and tool geometry/material

must be careful selected aiming to obtain best performance on the drilling operation, the

best hole quality, which represents minimal damage to the machined component and

satisfactory machined surface [1]

Figure 2.1 Principal aspects to be considered when drilling fibre reinforced

plastics.

2.3 PARAMETERS for DRILLING FIBER REINFORCED PALSTICS

2.3.1 Spindle Speed

The speed of a twist drill is generally referred to as cutting speed, surface speed,

or peripheral speed. It is the distance that a point on the circumference of a drill will

travel in 1 min. A wide range of drill and drill sizes is used to cut various metals an

equally wide range of speeds is required for the drill to cut efficiently. For every job,

there is the problem of choosing the drill speed that will result in the best production

rates and the least amount of downtime for regrinding the drill.

The most economical drilling speed depends on many variables:

(i) The type and hardness of the material

(ii) The diameter and material of the drill

(iii) The depth of the hole

(iv) The type and condition of the drill press

(v) The efficiency of the cutting fluid employed

(vi) The accuracy and quality of the hole required

(vii) The rigidity of the work setup

Although these factors are important in the selection of economical drilling

speeds, the type of work material and the diameter of the drill are the most important.

When references is made to the speeds at which a drill should revolve, the cutting speed

of the material in surface feet per minute (sf/min) or meters per minute (m/min) is

implied unless otherwise stated. The number of revolutions of the drill necessary to

attain the proper cutting speed for the metal being machined is called the revolutions per

minute (rpm). A small drill operating at the same rpm as larger drill will travel fewer

feet per minutes, it naturally would cut more efficiently at higher number of rpm [2].

The effect of the machining parameters is another important aspect to be

considered. Figure 3 shows the reported cutting parameters that are cutting speed and

feed rate typically employed when drilling polymeric composites using high speed steel

(HSS) and tungsten carbide (WC) drills. It can be seen that cutting speeds from 20 to

60 m/min are usually employed. Cutting speed is not a limiting factor when drilling

polymeric composites, particularly with hard metals, therefore, the use of cutting speeds

below 60 m/min may be explained by the maximum rotational speed of conventional

machining tools, since drill diameters above 10 mm are rarely reported. Another reason

for keeping cutting speeds below 60 m/min may reside in the fat that higher cutting

speed values lead to higher cutting temperature, which in turn may cause the softening

of the matrix [1].

Figure 2.2 Cutting speeds and feed rates typically employed when drilling

polymeric composites with high-speed steel (HSS) and tungsten carbide (WC)

drills.

2.3.2 Revolution per minute

To determine the correct number of rpm of a drill press spindle for a given size drill,

the following should be known:

(i) The type of material to be drilled

(ii) The recommended cutting speed of the material

(iii) The type of material from which the drill is made

Formula (Metric)

Rpm=CS(m)/πD(mm)

It is necessary to convert the meters in the numerator to millimeters so that both parts of

the equation are in the same unit. To accomplish this, multiply the CS in meters per

minute by 1000 to bring it to millimeters per minute.

Rpm= CS X 1000/ πD

Not all machines have a variable speed drive and therefore cannot be set to the

axact calculated speed. By dividing π(3.1416) into 1000, a simplified formula is derived

that is accurate enough for most drilling operations.

Rpm= CS X 320/D

2.3.3 Feed Rate

Feed is the distance that a drill advances into the work for each revolution. Drill

feeds may be expressed in decimals, fractions of an inch, or millimeters. Since the feed

rate is a determining factor in the rate of production and the life of the drill, it should be

carefully chosen for each job. The rate of feed is generally governed by:

(i) The diameter of the drill

(ii) The material of the workpiece

(iii) The condition of the drilling machine [2]

Investigated the influence of feed rate on the delamination of a glass fibre reinforced

plastic and found that under low feed rates delamination does not take place. When feed

rate is increased the actual back rake angle becomes negative, thus pushing the work

material instead of shearing and causing its delamination [3]. Refer to the Figure2.2,

whereas feed rate values lower than 0.3 mm/rev are frequent. The use of feed rates

below 0.3 mm/rev may be associated to the delamination damage caused when this

parameter is increased [1].

2.3.4 Thrust force and toque

We found that there is a delay between the response for thrust force and torque,

after which the former reaches a maximum value. From this point the thrust force value

is reduced probably due to the softening of the matrix caused by friction and the torque

increases due to the fact that the last fibres are not sheared, but entangled in the drill.

They also noticed that the effect of cutting speed on thrust force is negligible, whereas

torque increases with cutting speed. Surface roughness was not significantly affected by

both cutting speed and feed rate [4].

To machining of glass fibre reinforced plastics composites produced using

distinct matrix materials as a epoxy and polyester resins and reinforcing shapes like a

chopped, cross winding, continuous winding and woven. We found that in contrast to

other reinforcing shapes, when drilling the cross winding composite a gradual decrease

in thrust force was observed at the drill exit, resulting in a surface without delamination.

When machining the woven composite with different matrix materials, the matrix had a

negligible effect on thrust force but torque was higher when drilling the polyester

composite. Increasing cutting speed resulted in lower thrust force and torque due to the

higher temperatures produced by the increase in heat generation associated with the low

coefficient of thermal conduction together with the low transition temperature of plastics

[5].

The experiment involved drilling of a glass fibre reinforced plastic with a

cemented carbide drill (1 mm diameter). We found the thrust force is drastically reduced

when the hole is pre-drilled to 0.4 mm or above [6].

Figure 2.3 Influence of feed rate on the specific cutting coefficient (kf) associated

to the thrust force.

Figure 2.4 Influence of feed rate on the specific cutting coefficient (km)

associated to torque.

Figure 2.3 and Figure 2.4 show the influence of feed rate on the specific cutting

coefficients related to the thrust force (kf) and torque (km), respectively, calculated from

Equation,

Where:

(i) Ff is the thrust force (N)

(ii) f the feed rate (mm/rev)

(iv) d the drill diameter (mm)

(v) B is the torque (Nmm)

Noticed that from Figure 2.3 feed rate is increased, the kf values decrease at

higher feed rates. The number of fibres to be sheared will be reduced. Differences in the

kf values obtained for the same feed rate are due to differences in drill geometry,

reinforcing material, volume fraction, fibre orientation and laminate thickness. Figure

2.4 show the influence of feed rate on km for glass and carbon fiber reinforced plastics.

Similarly to Figure 2.3, it can be seen that for the same reasons previously explained, the

km values decreases drastically as feed rate is elevate.

2.4 MEASUREMENT OF THRUST FORCE AND TORQUE

Drilling tests were performed without backing plate and cutting fluid on

convention radial drilling machine. While the variable feed technique was implemented

on CNC milling/drilling machine. To neglect the effect of drill wear each hole was

drilled using a new standard HSS, coated carbide and carbide drills with 6 mm diameter.

Thrust force and torque was measured using two-component dynamometer, based on

strain-gage sensor Figure 2.5. The dynamometer was connected by a data acquisition

system that assembled in PC to monitor and acquire the test data. The data was stored as

an ASCII data file in the PC. These data represent the relationship between the

machining time and the electrical output signals from the strain gages that forming the

Wheatstone-bridges. The electrical output signals (volt) for thrust force and torque were

calibrated using known thrust and torque. The variation of thrust force and torque with

machining time were plotted as wave forms, while the average value of the maximum

five peaks in these wave diagrams were used to investigate the influence of cutting

variables on thrust force and torque. At least two testes were implemented for each

cutting variables. The drilling variables are: feed rate, f =1000, 2000, 3000 mm/min and

rpm= 1000, 3000, and 5000 [5].

Figure 2.5 Set-up for measurements the thrust force and torque.

2.5 TOOL MATERIAL AND GEOMETRY

Tool geometry is a relevant aspect to be considered in drilling of fiber-reinforced

plastics, particularly when the quality of the machined hole is critical. Finally, Figure 2.2

shows that tungsten carbide tools are preferred when drilling at higher cutting speeds

and at higher feed rates [1]. The influence of using a trepanning tool on thrust force and

torque when drilling glass fibre reinforced plastic showed that the performance of the

trepanning tool was superior to the conventional twist drill, resulting in 50 and 10% of

thrust force and torque [7]. Beside that, the effect of the drill diameter on the thrust force

and torque at a high speed twist drills with diameters of 8, 9, 10, 11, 12, and 13 mm to

machine a glass fibre reinforced plastic using a constant rotational speed of 875 rpm and

feed rates of 0.1–0.23 and 0.5 mm/rev. The results indicated that thrust force and torque

increased with drill diameter and feed rate, due to the increase in the shear area.

Increasing cutting speed also resulted in higher thrust force and torque, however, not to

the same extent as when feed rate is elevated [4].

Figure 6 presents the results of this survey with regard to the tool materials and

geometries used to drill polymeric composites. It can be seen that high-speed steel

(HSS) and tungsten carbide (ISO grades K10 and K20) are equally used as tool

materials, while polycrystalline diamond (PCD) is seldom tested. As far as the tool

geometry is concerned, it can be seen that the use of drill with special geometry such as

core drills, multi-facet drills, candle stick and parabolic drills together with drills with

modified geometry like a various chisel lengths and rake, clearance, point and helix

angles are preferred when drilling with tungsten carbide tools. On the other hand, when

using high-speed steel drills the use of standard twist drill and drills with special

geometry are similar.

Figure 2.6 Tool materials used to drill polymeric composites.

2.6 HOLE QUALITY AND PART PERFOMANCE

In the drilling of reinforced plastics the quality of the cut surfaces is strongly

dependent on the appropriate choice of drilling parameters. The aim of this work is to

clarify the interaction mechanisms between the drilling tool and material. Drilling tests

were carried out on glass-polyester composites using standard HSS tools. Drilling was

interrupted at preset depths to study damage development during drilling. The

specimens, polished by a metallographic technique, were examined by optical

microscopy to identify any damage. The results obtained are useful in describing the